Glasgow kids ‘are hemmed into a gang territory of a couple of featureless streets'. For many there is no escape. Photograph: William Thornton

We heard on Monday that in Glasgow, gang violence had dropped by 50% due to a groundbreaking new programme by Strathclyde police. This is great news for a city that's moved from being the murder capital of Europe to hosting the 2014 Commonwealth Games. The gang fights in Glasgow are a brutal form of sensation-seeking. On Friday nights undernourished white teenagers on the remote 1950s housing estates chase each other across uneven wasteground. It's dark; the rain is horizontal. One of them slips and falls. Then the air is alive with a fury of machetes, belt buckles, golf clubs and swords. Seventy-one murders a year. A serious facial injury every six hours.

These kids live and die in a square mile. They are hemmed into a gang territory of a couple of featureless streets. They cross the road to attack kids they hate because that's what their dad did. There's no way out. Many of these young boys never make it into the centre of Glasgow, with its cappuccino bars in Merchant City, the famed music scene of Glasvegas and 18-screen Imax. The only time they do is in an ambulance, racing down the Edinburgh Road to A&E all torn and slashed, to be stitched up by a facial surgeon.

The breakthrough came when Strathclyde police adopted a programme that had already reduced gang murders in the US. It offered the kids a way out. If they stopped the gang fights they'd have access to help with training, housing, education and community groups. If they carried on, they'd go to jail. It was the kind of choice a parent might give a child. The results speak for themselves. Four hundred gang members signed up. Violent offending among those who undertook the most intensive programme fell by 73%.

David Cameron take note. Gang interventions and youth services are being hit hard by the cuts. Any reform to criminal justice has been abandoned by the Tories as they face pressure from the red tops. The Tories are tending towards a more punitive approach to youth justice, shown by the six-month mandatory sentence for brandishing a knife. Yet traditional measures don't make sense when the jails are full and it costs £230,000 to keep a young man in a secure unit.

Strathclyde police had tried all traditional means of enforcement when they turned to the American model. They had had little success: crackdowns on knife-carrying and binge-drinking, stop-and-searches, and banning alcohol. The measures were short term only. Once a young offender is released he falls in with his old mates and is soon back in trouble. Kids grow up amid chronic deprivation, drug and alcohol addiction, and domestic violence. The only sensation-seeking they have is to swig some cheap cider and chase each other at the weekend with weapons. One boy was given a machete for his 13th birthday by his own mother.

It took a maverick to come up with the US gang programme. David Kennedy was a Harvard academic who wore hair down to the middle of his back. He'd wanted to be a writer for the New Yorker but felt a strong emotional and moral calling after seeing the crack-ravaged housing projects of Los Angeles in the 1980s. He decided it had to stop. Kennedy preferred to listen to drug dealers rather than academics, and the street became his classroom. With Boston gripped by an epidemic of teen homicides he realised that the really toxic thing was the group dynamics of the gang. Like a stag party or band of football hooligans, young men did far worse things when they were in groups. He decided to turn these group dynamics back on themselves.

He summoned the gang members to face-to-face forums in a Boston courtroom. In manacles and jumpsuits these menacing characters were reasoned with directly as adults. "Who thinks it is OK to kill 13-year-old girls?" they were asked. "How long will it take for your friend to sleep with your girlfriend when you're in jail ?" It gave them pause for thought. The most hard-hitting speakers were victims' mothers, who told them how their lives had been destroyed by the death of their son. Ex-offenders spoke about the dehumanising aspects of jail. Cops warned them if one of them committed an offence the whole gang would be punished. If they decided to leave the gang life they would be offered help with jobs, housing and training. It had a dramatic effect.

It took another maverick, Karyn McCluskey, the deputy chief at Glasgow's violence reduction unit, to bring the programme to the city. The results speak for themselves. She tried to kick-start the programme with the Metropolitan police but didn't gain enough support. And the Home Office recommended that Manchester should adopt the model in 2001, but the police there didn't believe it would work either.

Glasgow's programme uses existing resources in education, social services and housing. It received £750,000 of Scottish government funding every year for two years. If it keeps three offenders out of prison, it's paid for. It sounds as if it's already done far more than that – something Ken Clarke should consider as he tries to cut £2bn from his £8bn justice ministry budget.